The present invention relates to improved bulk polymerization reactor.
Emulsion polymerization process, suspension polymerization process, solution polymerization process and bulk polymerization process have been known as methods for industrially produce plastics on the basis of highpolymer forming reaction. Which process should be chosen is partly dependent upon what purpose the produced plastics are used for.
In general, however, the choice is greatly influenced by how to remove the heat of reaction and/or how to cope with the viscous material which increases as the polymerization reaction develops.
Among these processes, the bulk polymerization process is most advantageous since its easiness in constructing a closed system assures saving of resources and energy, and less polution of environment. In order to practice this process successfully on an industrial level, various problems have to be solved such as instability in reaction, abnormal stagnation of material whose viscosity increases exponentially as the polymerization develops, and reduction in surface for removal of heat which inevitably follows enlargement in construction of the reactor. For these reasons, this process is applicable to very limited types of plastics when compared with emulsion polymerization process, suspension polymerization process and solution polymerization process.
In general, viscosity of the system increases as the bulk polymerization develops and big difficulty is experienced in properly handling highly viscous materials. That is, abnormal stagnant layers grow in the area near the wall of the reaction chamber and/or the rotary mixer shaft. Such stagnation in the liquid phase at high temperatures tends to eventuate in deterioration of polymers with low heat stability such as colouring and, in the worst case, carbonization. Polymer in the stagnant layers is involved in the polymer flows in the liquid phase and causes undesirable colouring of the normal polymer and/or inclusion of carbonized spot in the normal polymer, thereby seriously lowering the commercial value of the produced plastics.
In order to preclude formation of such stagnant layers, a screw mechanism has been proposed in order to peel off the polymer stagnating near the wall of the reaction chamber. Use of a suitable kneading mechanism has been proposed also. Use of such conventional mechanisms requires considerably increased consumption of electric power. In addition, their movements in the reaction chamber generate high friction heat which naturally escalates temperature in the liquid phase in the reaction chamber. Such raised temperature in the liquid phase promotes deterioration of polymers of low heat stability. In addition, control of polymerization process in general becomes very difficult.
It is also proposed to complete the reaction whilst keeping low viscosity of the liquid phase without raising the conversion of polymerization. This method enables elimination of difficulty in stably handling the highly viscous liquid to be otherwise encountered in bulk polymerization process. With this method, however, one cannot expect high yield and simple recovery of monomers.
The conventional bulk polymerization reactor is accompanied with a further problem, i.e. instability of reaction. Polymerization reaction is in general a kind of exothermic reaction and high viscosity of the system disables easy control of the heat of reaction, thereby causing formation of hot spots and/or uncontrolled development in polymerization.